Carbon and chlorine isotope fractionation patterns associated with different engineered chloroform transformation reactions.

To use compound-specific isotope analysis for confidently [GRAPHIC] assessing organic contaminant attenuation in the environment, isotope fractionation patterns associated with different transformation mechanisms must first be explored in laboratory experiments. To deliver this information for the common groundwater contaminant chloroform (CF), this study investigated for the first time both carbon and chlorine isotope fractionation for three different engineered reactions: oxidative C-H bond cleavage using heat-activated persulfate, transformation under alkaline conditions (pH similar to 12) and reductive CCl bond cleavage by cast zerovalent iron, Fe(0). Carbon and chlorine isotope fractionation values were -8 +/- 1 parts per thousand and -0.44 +/- 0.06 parts per thousand for oxidation, -57 +/- 5 parts per thousand and -4.4 +/- 0.4 parts per thousand for alkaline hydrolysis (pH 11.84 +/- 0.03), and -33 +/- 11 parts per thousand and -3 +/- 1 parts per thousand for dechlorination, respectively. Carbon and chlorine apparent kinetic isotope effects (AKIEs) were in general agreement with expected mechanisms (CH bond cleavage in oxidation by persulfate, CCl bond cleavage in Fe(0)-mediated reductive dechlorination and E1(CB) elimination mechanism during alkaline hydrolysis) where a secondary AKIE(Cl) (1.00045 +/- 0.00004) was observed for oxidation. The different dual carbon-chlorine (Delta delta C-13 vs Delta delta Cl-37) isotope patterns for oxidation by thermally activated persulfate and alkaline hydrolysis (17 +/- 2 and 13.0 +/- 0.8, respectively) vs reductive dechlorination by Fe(0) (8 +/- 2) establish a base to identify and quantify these CF degradation mechanisms in the field